Neisseria gonorrhoeae is responsible for over 1 million cases of gonorrhea each year in the United States. The total health care costs associated with treating gonorrhea, and complications that arise from infections caused by this organism exceed 1 billion dollars per year. Gonococcal infections can disseminate, from the initial site of infection causing pelvic inflammatory disease (PID), which can lead to tubal infertility, ectopic pregnancy, and chronic pelvic pain, or into the blood stream causing disseminated gonococcal infections (DGI). Lipooligosaccharide (LOS) is a prominent surface antigen and a virulence factor that makes a major contribution to the pathogenesis of these diseases. LOS can exist as multiple chemically related components on a single cell, with variations in the oligosaccharide portion readily interconverting between forms. While one form of this molecule has been extensively studied, there are many other novel structures that are known to exist. The fact that this pathogen possesses so many different ways to manipulate its LOS, and can make such a diversity of structures, indicates that such modifications are important in pathogenesis. The objective of this proposal is to determine the genetic variability associated with LOS biosynthesis and determine if specific LOS structures are associated with specific clinical outcomes of infection by defining the structures expressed by the gonococcus and characterizing the molecular and functional basis for the modulation of the expression of these structures. The central hypothesis of the proposed research is that variation in the biosynthesis of LOS has additional genetic and biochemical underpinnings that have yet to be characterized, and that they lead to the synthesis of additional LOS structures that contribute to different biological properties of the bacterium. I will characterize the structural variability that exists in this species and will use the genetic information obtained to construct strains with invariant defined LOS. I will then analyze the biological significance of these structures by determining their contribution to serum resistance.